Known filling level measuring devices comprise parabolic antennas or horn antennas that transmit or receive radar waves or microwaves in order to determine the filling level of a medium in a filling level container. The antenna of such a filling level measuring device is, for example, arranged within the container.
For maximizing the antenna gain, the length of the antenna may be adjusted according to the frequency of the electromagnetic transmission signal used.
If the length of the antenna is reduced (without increasing the frequency of the transmit signal and without changing the aperture of the antenna), the antenna gain usually decreases and the intensity of secondary lobes increase.
In order to increase the antenna gain, a convex lens may be positioned at the end of the antenna horn, which lens may consist of a dielectric material. Such a lens changes the relative phase between microwaves which cross the lens in its outer region and microwaves which cross the lens in its centre, thus resulting in a phase correction between the two parts of the transmission signal, which in turn results in a more or less planar phase front of the transmission signal after it has left the antenna and the lens.
Such lenses are produced from an unmachined part by milling or lathing.